The one-electron oxidation and protonation of diferrocenylphenylphosphine (Fc2PhP) leads to the formation of two distinct, stable cationic phosphorus species, namely the radical cation Fc2PhPB(C6F5)4 and the phosphonium ion Fc2PhPHB(C6F5)4. Although their solid-state structures are remarkably similar, the bathochromic shift in the UV-Vis absorption spectrum of the radical cation, signals with distinct multiplicities in the 31P NMR spectra, as well as contrasting quadrupole splitting values in the 57Fe Mößbauer spectra, elucidated the differences between the two cations.
Stoian et al. (2025) studied this question.